Basic Information

An ordnance class gun of calibre greater than or equal to 20mm from the most primitive muzzle-loadingblack powder weapons to cutting edge technology. Doesn't apply - except euphamistically - to small arms. Some sources suggest that a cannon should not be capable of fully automatic fire, but given the large number of automatic cannon that are, or have been, in service over the years this distinction seems to have gone by the board.

In strictest terms a cannon should also only fire at elevations between zero and forty-five degrees from the horizontal - becoming a howitzer if it fires between zero and ninety and a mortar if it is limited to elevations of between forty five and ninety. This definition also went by the board rather with the invention of anti-aircraft mounts and is not much observed in the modern era - although the term howitzer is still used for cannon capable of high-angle fire.

Can overlap with heavy weapons in some cases - such as the French M1916 37mm Infantry Gun (derivatives of which were issued by the Japanese and US Forces) or some of the heavy anti-tank rifles common in WW2 such as the Japanese Type 97 or the Solothurn S-18/1000. If in doubt, these cases are referred back to the idea that a cannon is ordnance and as such a man-portable weapon is not a cannon (even if called a "hand-cannon").